1. Field of the Invention
The present invention relates in general to a helical pier which utilizes pressurized grouting to stabilize a section of soil to increase the helical pier's supporting characteristics, such as when used with old construction, with new construction, in tie-back applications and the like.
2. Description of the Related Art
In the past, systems have been proposed in which piers, pilings, and the like are anchored into the earth and used to support various structures, such as walls, bridges, and buildings. One system has been proposed (U.S. Pat. No. 3,999,391) in which a tie-back anchor is drilled into non-excavated, undisturbed earth and used to support upstanding shoring walls through a plurality of tension cables. The anchor is formed from a hollow tubular element having helical flighting elements thereon for pulling the anchor into place. Multiple load transfer pins extend inwardly through the tube walls. Once in place, loose cables with bushings locked on the lower ends thereof are lowered into the hollow tube. The cables are staggered such that the bushings are distributed along the anchor's length. Next, the tube is filled with grout and, once hardened, serves to transfer tension loading from the cables to the load transfer pins and the tube.
However, tie-back anchors of this type were ineffective in regions of earth which were uncompressed or otherwise naturally unstable. Further, anchors of this type necessitated the use of non-corrosive (e.g., galvanized) tubing to prevent deterioration of the anchor.
An alternative system has been proposed (U.S. Pat. No. 3,738,071) in which a pre-stressed tension anchor is constructed by initially drilling a bore hole into the ground. A tension member, including steel bars arranged in a radially symmetrical manner and separated by spacers is lowered into the bore hole. Next, the hole is filled with a cement glue and once hardened, the cement glue and tension member form an anchor. A similar tie-back anchor has been proposed (U.S. Pat. No. 4,718,791) having a unitary hollow casing connected to a drill. Pre-stressing steel tendon is inserted within the casing and a lost bit is affixed to a bottom end of the casing. The drill and casing are then positioned in the desired location and the casing is rotated into the ground by the drill while fluid, such as air or water, is used to remove the soil from the region surrounding the casing as the casing is advanced. Once the casing has been drilled to the desired depth, and a cavity has been formed thereabout, the bit is released and grout is pumped through the casing into the cavity. Then the casing is removed from the hole before the grout hardens, thereby leaving a bit within the grout and affixed to the pre-stressing steel tendon.
In two alternative systems (U.S. Pat. Nos. 1,270,659 and 4,830,544) tie-back anchors are provided which utilize tubing to inject grout into the ground and which leave tubing in the hole with the grout. The '544 patent discloses a tie-rod anchor which is inserted into a previously formed hole. The tie-rod includes a tube which is separated into five distinct sections coupled to one another with fittings. A valve fitting initially directs grout to a flexible bag formed about an uppermost outlet fitting to initially fill the bag and seal off the top of the hole. Once the hole is sealed, the valve fitting opens and allows a remainder of the grout to be injected into the hole through outlet fittings. In the '544 patent, a cable is mounted beside the tube and secured to the grout to enable the anchor to be coupled to a desired structure.
The system of the '659 patent is used to reinforce retaining walls, such as used in harbors and wharfs. In the system of the '659 patent, a piling is driven into the earth and filled with concrete. The piling is tubular in structure, perforated, and includes an open bottom end. The tube may be inserted into the ground by inserting a boring tool through the tube. As the boring tool makes the hole, the tube is forced into place thereafter with the earth being withdrawn at the top of the tube.
However, the tubing of the '544 and '659 patents do not serve as the primary anchoring force. Further, the systems of the '791, '544, '071, and '659 patents require that earth be excavated out of the way before concrete is injected. Also, the prior art systems require multiple steps to insert and utilize the anchors. The systems of the '659, '791, '544, and '071 patents require separate drilling tools to bore the hole in which the anchor is inserted. Further, the systems of the '791, '544, and '071 patents utilize cables imbedded within concrete to provide the primary anchoring force.
While the system of the '391 patent provides an anchor which is sinkable without a separate drill, this anchor relies exclusively on the integrity of the earth and flightings upon the anchor. Further, the anchor of the '391 patent requires a complex internal cable assembly projecting from the anchor to provide tension loading, which must be installed after the anchor is sunk.
Systems have been proposed for sinking underpinnings to support new and old structures, such as buildings, bridges, patios, and the like. Exemplary systems are disclosed in U.S. Pat. Nos. 4,634,319, 4,800,700, 4,854,782, 5,011,336, 5,120,163, 5,139,368, 5,171,107, and 5,213,448. These systems sink pilings or helical underpinnings along the foundation of an existing structure which has settled. The pilings and underpinnings are sunk to bedrock or a load-bearing strata which is able to provide sufficient support throughout the life of the structure. Once sunk, the pilings or underpinnings are used as bases to support an equal number of hydraulic jacks which include rams fastened to the foundation through brackets. The rams are used to raise the building. The building is affixed at this raised height by securing the brackets to the pilings or underpinnings.
However, when the pilings or helical underpinnings are used in soils having a weak load-bearing capacity, they must be sunk to a substantial depth. Thus, a significant amount of materials and labor are needed to sink multiple piers. To reduce the necessary depth, the piling and helix diameters must be increased. However, this requires additional driving force.
Further, when loads are placed on the piling or helical underpinning, the uppermost end thereof sinks slightly under the weight of the structure. This phenomenon is commonly referred to as deflection and results when the piling laterally bends or bows underground as a load is applied. Lateral deflection varies depending upon the amount of lateral support offered by the soil. When drilling a helical underpinning into the ground, the helixes thereon disturb and disrupt the soil surrounding the underpinning. Thus, helical underpinnings may experience substantial lateral deflection. Such deflect is undesirable since it reduces the load-bearing capacity of the underpinning and requires an allowance therefore when calculating the level at which to secure the foundation to the underpinning. Also, each underpinning will experience a different amount of deflection, and thus provides varying amounts of support for the foundation.
Moreover, piers supporting new and existing structures and tie-back applications frequently experience large lateral forces which are caused by earthquakes, lateral earth pressures, and the like. The piers or pilings must be able to resist these lateral forces. In some areas, building codes require that the piles are capable of resisting a lateral force equal to 10% of the applied axial load. Piles serving as tie-backs to support retaining walls, abutments, rigid frame bridges, locking structures, and the like, also frequently experience high lateral forces. These lateral forces may be resulted from lateral earth pressures acting upon the retaining structure or from differential fluid pressures acting upon the locking structure. Additional lateral forces may result from horizontal thrust loads acting on abutments of fixed or hinged arched bridges. The lateral support capacity of such piles varies depending upon the cohesiveness of the soil with more cohesive soil providing more lateral support.
Additionally, once a conventional pier or helical underpinning is sunk into the ground, during rain storms, rainwater collects around the top of the shaft. The outside surface of shaft serves as conduit to direct this water downward about its perimeter. As the rainwater migrates down the shaft, it soaks into the surrounding soil and reduces the cohesion characteristics between the pier/underpinnings and the surrounding soil. The migrating rain water also travels along the surface of helixes, further interfering with the transfer of loads between the helixes and the soil. Also, certain gypsiferous soils and the like, include a composition having water soluble materials (salt and the like) therein which, when dry, contribute substantially to the load bearing capacity of the soil. As the rainwater leaches through this soil proximate the helixes, these soluble materials are displaced with the water. Hence, as the rainwater soaks outward, certain soils afford a lesser load bearing structural value when wet.
Hereafter, tie-back anchors and underpinnings are collectively referred to as "pier columns". Also, hereafter new and old construction supported by underpinnings and structures held by tie-backs are collectively referred to as "structures".
The need remains within the industry to provide an improved anchoring assembly and method of use therefor to overcome the disadvantages heretofore experienced. The present invention is intended to satisfy this need.